The column widget of Webflow will not allow text to pass from a columns to another. You can try to make it work but it's more for layout than text.
There's a column CSS property but I guess it's not in webflow by default because it still is badly supported by some browsers. However, when it doesn't work, it degrades nicely by just displaying a box of text, without columns.
You can add the CSS to the head of your site in the settings.
-webkit-column-count: 3; /* Chrome, Safari, Opera */
-moz-column-count: 3; /* Firefox */
Add columns as a class to a paragraph, it should split into 3 columns.
There are more options like gutter size and rulers available http://www.w3schools.com/css/css3_multiple_columns.asp
This should not work in Preview mode, only when published I guess.
Edit, it works (: http://sab.webflow.com/columns
Edit: don't name your class "3columns", put the digit at the end